Abstract: The influences of the modified polypropylene (PP) fiber and the hybrid ratio and hybrid effect of PP fiber and aramid fiber on the mechanical properties of cement-based composites were investigated. The physical models of the interface layer of fiber and cement mortar were built in order to describe the fiber reinforced mechanism of the cement mortar. The experiments show that the modified PP fiber improves the earlier flexural strength of cement mortar obviously, and the mixture of PP fiber and aramid fiber increases the later flexural strength of cement mortar significantly. The 3 days and 28 days flexural strength of the cement mortar, which reinforced by the mixture of 0.56% volume fraction of PP fiber and 0.24% volume fraction of aramid fiber, are increased by 18.48% and 31.17% compared to its ordinary cement mortar, respectively, and its 3 days and 28 days compressive strength are increased by 7.16% and 5.19%, respectively.